Life at the top: Bill Baroni, deputy executive director of the Port Authority of New York and New Jersey, speaks to the media on the 71st floor of One World Trade Center One World Trade Center, the giant monolith being built to replace the twin towers destroyed in the September 11 attacks, today laid claim to the title of New York City's tallest skyscraper.At 2pm, workers erected steel columns that made its unfinished skeleton 1,251 feet high, just enough to peak a foot over the roof of the observation deck on the Empire State Building.The New York Port Authority and building owners also held a press conference in which they officially celebrated the landmark moment.

Room with a view: Workers sit on one of the top floors of the new One World Trade Center building

The view from one of the top floors of the new One World Trade Center

The magic moment: Workers lower the girder that made One World Trade Center the highest building in New York today

Tallest in New York: The girder is succesfully installed at the top of One World Trade Center making it the tallest building in New York

Tricky: A crane on the top of the massive skyscraper lifts a steel beam into place on the 100th floor of the new World Trade Center building

Success: Steel workers Billy Geoghan and Jim Brady walk on the steel beam which gave One World Trade Center bragging rights over the rest of New York

Looking down on the world: View from the 71st floor of One World Trade Center

Pin point: Spires, however, are considered part of the building and are always counted. It's a tradition that goes back to a time when the tallest buildings in many European cities were cathedrals

Still growing: Workers are still adding floors to the so-called 'Freedom Tower' and the building isn't expected to reach its targeted 1,776 foot height for another year

However, the milestone is a preliminary one. Workers are still adding floors to the so-called 'Freedom Tower’ and it isn't expected to reach its full height for at least another year.At which point it is likely to be declared the tallest building in the U.S., and third tallest in the world.Those bragging rights, though, will carry an asterisk.Crowning the world's tallest buildings is a little like picking the heavyweight champion in boxing. There is often disagreement about who deserves the belt.

Life on top: A view of One World Trade Center from the Rockefeller Center today

Soaring: One World Trade Center overlooks Battery Park City and the Hudson

As it used to be: The Manhattan skyline before the destruction of the original World Trade Center in the September 11 attacks

Consider the case of the Empire State Building: Measured from the sidewalk to the tip of its needle-like antenna, the granddaddy of all super-tall skyscrapers actually stands 1,454 feet high, well above the mark being surpassed by One World Trade Center on Monday.Purists, though, say antennas shouldn't count when determining building height.An antenna, they say, is more like furniture than a piece of architecture. Like a chair sitting on a rooftop, an antenna can be attached or removed.The Empire State Building didn't even get its distinctive antenna until 1952. The record books, as the argument goes, shouldn't change every time someone installs a new satellite dish.

Rising high: One World Trade Center is now higher than the observation platform of the Empire State Building

Excluding the antenna brings the Empire State Building's total height to 1,250 feet. That was still high enough to make the skyscraper the world's tallest from 1931 until 1972.From that height, the Empire State seems to tower over the second tallest completed building in New York, the Bank of America Tower.Yet, in many record books, the two skyscrapers are separated by just 50 feet.That's because the tall, thin mast on top of the Bank of America building isn't an antenna, but a decorative spire.

City landmark: Pedestrians cross 14th street in view of One World Trade Center

Unlike antennas, record-keepers like spires. It's a tradition that harkens back to a time when the tallest buildings in many European cities were cathedrals.Groups like the Council on Tall Buildings, and Emporis, a building data provider in Germany, both count spires when measuring the total height of a building, even if that spire happens to look exactly like an antenna.This quirk in the record books has benefited buildings like Chicago's recently opened Trump International Hotel and Tower.

Beacon of hope: One World Trade Center - the lit-up building on the left - will lay claim to the title of New York City's tallest skyscraper on Monday

It is routinely listed as being between 119 to 139 feet taller than the Empire State Building, thanks to the antenna-like mast that sits on its roof, even though the average person, looking at the two buildings side by side, would probably judge the New York skyscraper to be taller.The same factors apply to measuring the height of One World Trade Center.Designs call for the tower's roof to stand at 1,368 feet - the same height as the north tower of the original World Trade Center. The building's roof will be topped with a 408-foot, cable-stayed mast, making the total height of the structure a symbolic 1,776 feet.

Tall order: Without a spire, the completed One World Trade Center would be smaller than Chicago's Willis Tower at 1,451 feet but bigger than the Empire State Building at 1,250 feet (not including antennas)